1. Field Of The Invention
The present invention generally relates to a graft copolymer, a solution containing the graft copolymer for treating a contact lens, and a method of treating a contact lens with the solution and making a hydrophilic lens surface. In particular, the present invention relates to a novel graft copolymer suitable for modifying a hydrophobic surface into a hydrophilic surface, technique of modifying into a hydrophilic surface a hydrophobic surface of a non-water absorbable or swellable contact lens such as a hard contact lens and a non-water swellable soft contact lens, and a contact lens treatment solution containing the graft copolymer which solution is suitably used for the technique.
2. Related Art Statement
There have conventionally been used a non-water absorbable or swellable contact lenses, such as a hard contact lens made mainly from methyl methacrylate, a high-degree oxygen permeable hard contact lens made mainly from siloxanylalkyl methacrylate, fluoroalkyl methacrylate, etc., and a non-water swellable soft contact lens formed of silicone rubber made mainly from polydimethylsiloxane or butyl rubber made mainly from butyl acrylate.
The surface of non-water swellable contact lens is hydrophobic. In particular, the degree of hydrophobicity of the high-degree oxygen permeable contact lens, which has recently come to public notice, is extremely high. For improving permeation of oxygen through a contact lens, there is the tendency of forming the lens by using a material containing an increased amount of silicone or fluorine. Accordingly, a contact lens capable of higher degree oxygen permeation contains a greater amount of silicone or fluorine. For this reason, the surface of high-degree oxygen permeable contact lens has high degree of hydrophobicity. Because of the high degree of hydrophobicity, lipid particles contained in tears easily cling to the lens surface, thereby fouling the surface and causing the lens to be bloomed. Consequently, the user or wearer loses a clear sight.
For modifying the hydrophobic lens surface into a hydrophilic surface, the contact lens may be subjected to the plasma surface treatment, or the chemical treatment using an acid, an alkali, etc. However, those methods suffer from low durability of the hydrophilic surface produced. In addition, it is time-consuming and troublesome to carry out each method on the contact lens later.
Further, there is known the wetting solution method in which a contact lens is immersed in a solution containing a hydrophilic polymer so that the polymer entities adhere to the lens surface and thereby modify the hydrophobic lens surface into a hydrophilic surface. This method permits, if necessary, repetitive treatment of the contact lens, and the hydrophilic lens surface is easily maintained.
An example of the wetting solution method is disclosed in Japanese Patent Application laid open for opposition purpose under Publication No. 48-37910 (1973). The disclosed method utilizes a contact lens treatment solution containing a water soluble polymer such as polyvinyl alcohol, hydroxyethyl cellulose, and poly vinylpyrrolidone. The treatment solution is effective for a contact lens with low degree of hydrophobicity, such as a hard contact lens made from methyl methacrylate and a high-degree oxygen permeable hard contact lens made mainly from methyl methacrylate. However, the solution is not effective for treating a contact lens with high degree of hydrophobicity, such as non-water swellable contact lens made from material containing a large amount of silicone or fluorine, because the polymer entities dissolved in the solution do not sufficiently adhere to the lens surface due to the high hydrophobicity thereof.
In addition, Japanese Patent Application laid open under Publication No. 63-246718 (1988) discloses a contact lens treatment solution containing a polymer with ionic electric charge. For using the treatment solution, however, it is needed that the contact lens surface to be treated therewith have electric charge whose sign is opposite to that of the polymer contained in the solution, and that the density of the opposite electric charge is higher than a certain level. Accordingly, an additional step of increasing the electric charge density on the lens surface is required before the step of solution treatment. This treatment method is therefore time-consuming and complex. As can be read from the detailed description of the patent document, the method needs a relatively long time, e.g., five minutes. Further, the disclosed solution is not satisfactory with respect to the capability of modifying a hydrophobic lens surface into a hydrophilic surface. Thus, the disclosed solution suffers from some disadvantages.